Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, and various signal processing circuits.
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual images for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
FIG. 1 illustrates electronic device 50 having a chip carrier substrate or printed circuit board (PCB) 52 with a plurality of semiconductor packages mounted on a surface of the PCB. Electronic device 50 can have one type of semiconductor package, or multiple types of semiconductor packages, depending on the application. Different types of semiconductor packages are shown in FIG. 1 for purposes of illustration.
Electronic device 50 can be a stand-alone system that uses the semiconductor packages to perform one or more electrical functions. Alternatively, electronic device 50 can be a subcomponent of a larger system. For example, electronic device 50 can be part of a tablet, cellular phone, digital camera, television, power supply, or other electronic device. Electronic device 50 can also be a graphics card, network interface card, or other expansion card that is inserted into a personal computer. The semiconductor packages can include microprocessors, memories, application specific integrated circuits (ASIC), programmable logic circuits, analog circuits, radio frequency (RF) circuits, discrete devices, or other semiconductor die or electrical components.
In FIG. 1, PCB 52 provides a general substrate for structural support and electrical interconnect of the semiconductor packages mounted on the PCB. Conductive signal traces 54 are formed over a surface or within layers of PCB 52 using evaporation, electrolytic plating, electroless plating, screen printing, or another suitable metal deposition process. Signal traces 54 provide for electrical communication between each of the semiconductor packages, mounted components, and other external system components. Traces 54 also provide power and ground connections to each of the semiconductor packages. A clock signal is transmitted between semiconductor packages via traces 54 in some embodiments.
For the purpose of illustration, several types of first level packaging, including bond wire package 56 and flipchip 58, are shown on PCB 52. Additionally, several types of second level packaging, including ball grid array (BGA) 60, bump chip carrier (BCC) 62, land grid array (LGA) 66, multi-chip module (MCM) 68, quad flat non-leaded package (QFN) 70, quad flat package 72, embedded wafer level ball grid array (eWLB) 74, and wafer level chip scale package (WLCSP) 76 are shown mounted on PCB 52. Depending upon the system requirements, any combination of semiconductor packages, configured with any combination of first and second level packaging styles, as well as other electronic components, can be connected to PCB 52.
A manufacturer of electronic device 50 provides a power signal to the electronic device which is used to power the semiconductor packages and other devices disposed on PCB 52. In many cases, the provided power signal is at a different voltage than the voltage required to operate the individual semiconductor devices. The manufacturer will generally provide a power converter circuit on PCB 52 to generate a steady direct current (DC) voltage signal at a voltage potential level usable by the individual semiconductor packages. One topology that is commonly used for medium and high power converters is the series LLC resonant mode converter, which is a type of switch-mode power supply (SMPS).
A circuit diagram for one exemplary embodiment of an LLC resonant mode converter 100 is illustrated in FIG. 2a. LLC resonant mode converter 100 has a primary side 102 and a secondary side 104. Primary side 102 includes a voltage source 106, which is a DC voltage source. In one embodiment, voltage source 106 is an AC main line distributed by a power company or municipality to a power outlet at a user's home or office that is rectified to DC, e.g., by a diode bridge. Voltage source 106 is coupled between ground node 108 and circuit node 110. Primary side 102 also has high side MOSFET 112 with a drain terminal coupled to circuit node 110, a gate terminal 114, and a source terminal coupled to MOSFET 116 at half-bridge (HB) node 122. Low side MOSFET 116 includes a drain terminal coupled to the source terminal of MOSFET 112 at HB node 122, a gate terminal 118, and a source terminal coupled to ground node 108.
Primary side 102 of LLC resonant mode converter 100 includes resonant inductor 128, resonant capacitor 136, and the primary side of transformer 130, including primary winding 132 and magnetizing inductance 134, coupled in series between HB node 122 and ground node 108. Resonant inductor 128, primary winding 132, magnetizing inductance 134, and resonant capacitor 136 form an LLC tank for LLC resonant mode converter 100. A controller drives the LLC resonant tank formed by resonant inductor 128, primary winding 132, magnetizing inductance 134, and resonant capacitor 136 by turning MOSFETs 112 and 116 on and off alternatively using gates 114 and 118. A controller turns MOSFET 112 on by applying a positive voltage at gate terminal 114, and turns MOSFET 112 off by applying a ground voltage potential to gate terminal 114. A controller turns MOSFET 116 on by applying a positive voltage at gate terminal 118, and turns MOSFET 116 off by applying a ground voltage potential to gate terminal 118.
MOSFETs 112 and 116 are n-channel MOSFETs, indicating that negative carriers, or electrons, are the majority carrier for electric current through the MOSFETs. In other embodiments, p-channel MOSFETs are used that have positive electron holes as the majority carrier. An n-channel MOSFET provides low electrical resistance between a drain terminal and a source terminal of the n-channel MOSFET when a voltage potential of a gate terminal is sufficiently high. With the gate of the MOSFET at ground potential, or at least below a threshold, a larger electrical resistance is exhibited between the drain and source of the MOSFET.
In the ideal case, an n-channel MOSFET exhibits zero resistance when its gate has a positive voltage potential, and exhibits infinite resistance when its gate is at ground potential. MOSFETs 112 and 116 operate as switches which are opened and closed by control signals from a controller coupled to the MOSFETs' respective gates. A switch, e.g., MOSFETs 112 and 116, being closed is also referred to as the switch being “on,” because electric current is able to flow between terminals of the switch. An open switch is referred to as being “off” because current does not flow significantly between terminals of the switch. While the switches of LLC resonant mode converter 100 are illustrated as MOSFETs, other types of electronically controlled switches, e.g., bipolar-junction transistors (BJTs), are used in other embodiments. MOSFETs include source and drain terminals, which are conduction terminals, and a gate terminal as a control terminal. BJTs include emitter and collector terminals, which are conduction terminals, and a base terminal as a control terminal.
When MOSFET 112 is on and MOSFET 116 is off, HB node 122 is coupled to a positive voltage at circuit node 110 through MOSFET 112. When MOSFET 116 is on and MOSFET 112 is off, HB node 122 is coupled to ground node 108 through MOSFET 116. The switching of MOSFETs 112 and 116 causes the voltage potential at HB node 122 to alternate between the voltage potential of voltage source 106 and ground potential. The pulsating voltage potential at HB node 122 causes resonant inductor 128, primary winding 132, magnetizing inductance 134, and resonant capacitor 136 to resonate.
Magnetizing inductance 134 is not an actual physical inductor, but is used in analysis to represent a portion of current through transformer 130 that is used to magnetize core 137. Energy is transferred from primary winding 132 to secondary winding 138 through magnetic coupling. A certain percentage of the power input to transformer 130, analyzed as the current through magnetizing inductance 134, is lost in core 137 because the core does not have a perfectly efficient magnetic response.
As HB node 122 toggles between ground voltage and the voltage potential of voltage source 106, power is transferred from primary winding 132 to secondary winding 138. A circuit node 152 is connected to secondary winding 138 as a center-tap. A secondary winding portion 138a is coupled between center tapped circuit node 152 and diode 142, while secondary winding portion 138b is coupled between center tapped circuit node 152 and diode 144. Diodes 142 and 144 rectify the current through secondary winding 138. Capacitor 146 is coupled between circuit node 150 and circuit node 152 to filter the voltage to a more steady DC voltage.
FIG. 2b illustrates timing diagrams of voltages and currents at various circuit nodes of LLC resonant mode converter 100 through a full power transfer cycle. Time is illustrated on the X, or horizontal, axis, and voltage or current magnitude is illustrated on the Y, or vertical, axis. Time is not labelled in units of time, but rather to distinguish between modes of operation of LLC resonant mode converter 100.
Signal 154 in FIG. 2b represents a signal generated by a controller integrated circuit (IC) and routed to gate 114 of MOSFET 112. Signal 154 goes from logic zero to logic one, or from ground voltage to a positive voltage, at time zero. Signal 154 at a positive voltage turns on MOSFET 112, which couples HB node 122 to the voltage at circuit node 110. Signal 154 returns to a logic zero, or ground potential, at time 2.
Signal 155 in FIG. 2b represents a signal generated by a controller IC and routed to gate 118 of MOSFET 116. Signal 155 transitions from a logic zero to a logic one at time 3, and returns to logic zero at time 5. Signal 155 at a positive voltage turns on MOSFET 116, which couples HB node 122 to ground node 108.
Primary current 156 in FIG. 2b is the total current through the primary side of transformer 130, i.e., the current through magnetizing inductance 134 summed with the current through primary winding 132. Magnetizing current 157 is the current through magnetizing inductance 134 that is used to magnetize core 137 of transformer 130. Beginning at time zero, currents 156 and 157 increase from negative values to positive values due to coupling to positive voltage at circuit node 110 through MOSFET 112. The arc of primary current 156 illustrates resonance between resonant capacitor 136 and resonant inductor 128. Prior to time 1, while primary current 156 is negative, the body diode of MOSFET 112 conducts and allows signal 154 to turn on MOSFET 112 under zero voltage switching (ZVS) conditions.
The difference between total primary current 156 and magnetizing current 157 is transferred to secondary winding 138. The reflected current in secondary winding 138 is illustrated as secondary current 158 in FIG. 2b. Secondary current 158 is determined based on a difference between primary current 156 and magnetizing current 157. The magnetizing current 157 portion of primary current 156 is used to magnetize core 137, while the remaining portion of primary current 156 is reflected as secondary current 158. Secondary current 158 is only illustrated as including positive values because negative current is rectified to positive voltage at circuit node 150 by diodes 142 and 144.
At time 2, signal 154 returns to ground voltage potential, shutting off MOSFET 112. Currents 156 and 157 reverse direction and the body diode of MOSFET 116 conducts to ground node 108. Currents 156 and 157 fall from a positive value to a negative value due to the coupling to ground node 108, mirroring the currents between time 0 and time 2. Signal 155 turns on MOSFET 116 at time 3, while primary current 156 remains positive, to achieve ZVS. Secondary current 158 includes a positive pulse between time 3 and time 5 due to rectification by diodes 142 and 144. Secondary current 158, which flows through either diode 142 or diode 144 to circuit node 150, charges capacitor 146 and powers a load attached between circuit nodes 150 and 152.
LLC resonant mode converters are commonly used for medium and high power converters because of high efficiency and power density. In higher power circuits, power factor correction (PFC) front-end circuitry is used to regulate the voltage potential of voltage source 106. LLC resonant mode converters are also used in some low power devices. LLC resonant mode convert 100 may be used without a PFC front-end in some embodiments, commonly low-power applications, to increase efficiency. However, without a PFC front-end, LLC resonant mode converter 100 receives a wide range of input voltages at circuit node 110. For instance, LLC resonant mode converter 100 may be plugged into a 120 Volt outlet in the United States, or a 230 Volt electrical outlet in Europe. Higher input voltages increase the maximum power output of LLC resonant mode converter 100. LLC resonant mode converter 100 can be designed to compensate for variable input voltage by limiting output power to an approximately constant value over a range of input voltages, referred to as over power protection (OPP). OPP systems for LLC resonant mode converter 100 limit the current through MOSFET 112, MOSFET 116, transformer 130, diode 142, diode 144, and other circuit elements at higher input voltages to protect the parts from overheating and damage.
One useful piece of information in OPP systems for LLC resonant mode converters is the input power of the converter. An input power calculation is performed to determine whether input power is over a threshold and should be reduced by the OPP system. However, calculating an accurate power input level of LLC resonant mode converter 100 while ignoring magnetizing current 157 through transformer 130 presents a challenge.